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Abstract:

A processing technology is for the fabrication at low temperatures of
ferroelectric crystalline oxide thin films, among others
PbZrxTi1-xO3 (PZT) (<400° C. for PZT) with
ferroelectric properties appropriate for integration in devices. The
method is also for the fabrication of ferroelectric thin films of bronze
tungsten (A2B2O6), perovskite (ABO3), pyrochlore
(A2B2O7) and bismuth-layer (Bi4Ti3O12)
structures, in which A and B are mono, bi-, tri-, tetra- and pentavalent
ions. The method is based on the combination of Seeded Diphasic Sol Gel
(SDSG) precursors with Photo Chemical Solution Deposition (PCSD)
methodology and comprises the main following steps: i) synthesis of a
modified metal-organic precursor solution of the desired metal oxide
composition with a large photo-sensitivity in the UV wavelength range;
ii) preparation by a sol gel process of nanoparticles of the desired
composition, similar or dissimilar to the crystalline compound to be
obtained from the previous precursor sol; iii) dispersion of the
crystalline nanoparticles in the precursor sol to prepare a stable and
homogeneous sol-gel based suspension; iv) deposition of the previous
suspension onto substrates; v) UV irradiation in air or oxygen of the
deposited layer and further thermal treatment in air or oxygen of the
irradiated layer at temperatures below 400° C. The method provides
for the fabrication of polycrystalline ferroelectric, piezoelectric,
pyroelectric and dielectric thin films, dense and without cracks with
thickness above 50 nm and below 800 nm on single crystal,
polycrystalline, amorphous, metallic and polymeric substrates at low
temperatures and with optimised properties, being applicable in
microelectronics and optics industries.

3. The method according to claim 1, wherein the solution deposition
occurred by forming a thin layer by spinning or dipping the mixed
suspension onto a substrate and where the layer comprises from about 0.5
to 10 weight percent of the perovskite nano powder and are about 100
nanometer or less in thickness, wherein the weight percentage is the
metal concentration of the solution, and the layer has the same
percentage.

4. The method according to claim 1, wherein the drying of the deposited
layer being occurred on a hot-plate at 302.degree. F. (150.degree. C.)
for less than 15 minutes and further exposure to ultraviolet irradiation
in air or oxygen rich atmosphere and for a period of time from 1 to 5
hour, sufficient to evaporate and eliminate the majority of the organic
species.

5. The method according to claim 1, wherein the synthesis of
photosensitive solution precursors occurs by the modification of metal
alkoxide reagents with β-diketonate compounds or other organic
ligands.

6. The method according to claim 5, wherein the solutions comprising
coordination complexes of transition metals, the complexes being
photo-sensitive.

7. The method according to claim 6, wherein the mentioned complexes of
metals are selected from the group of compositions consisting of
derivates from titanium and zirconium alkoxides, or metal alkoxides
modified with β-diketonate compounds or other organic ligands.

9. The method according to claim 8, wherein the metal acetates are
dissolved in acetic acid.

10. The method according to claim 8, wherein the metal alkoxides are
modified with acetylacetone.

11. The method according to claim 5, wherein the base solution containing
glycols and alcohols as solvents and the element concentration are within
the range 0.2-0.4M.

12. The method according to claim 1, wherein mixing the photosensitive
sol-gel solution with up to about 10% weight of the ferroelectric
nanoparticles selected from the group, with ferroelectric composition,
wherein the particle size of the obtained ceramic powders is less than
100 nm, and produces a uniform stable dispersion.

13. The method according to claim 12, wherein the nanoparticles having a
same crystalline phase and a same element composition of the sol-gel
solution.

14. The method according to claim 10 wherein the nanopowders having a
same or different crystalline phase and a different elemental composition
of the sol-gel solution.

15. The method according to claim 11, wherein the nanoparticle
compositions are selected from the group consisting of compositions
having the same or different crystalline phase and different element
composition, from the family of perovskite, pyrochlores and bismuth
layer.

16. The method according to claim 15 wherein the nanoparticle
compositions are compounds are selected from the group consisting of:
BaxSr1-xTiO3, being x from [0 to 1],
PbZrxTi1-xO3, being x from 0 to 1, CaTiO3,
MgTiO3, NaxTi1-xTiO3 being x from 0 to 1,
(1-x)K.sub.0.5Na.sub.0.5NbO3 (KNN)-xLiTaO3 being x from 0 to 1,
Bi4Ti3O12, among others.

17. The method according to claim 16, wherein the ceramic powders have a
concentration comprised between 0.5 and 10 wt % of the solute in the sol
precursor.

18. The method according to claim 17, comprising a further step of
ultrasonic stirring, reducing agglomeration of particles.

19. The method according to claim 18, comprising a stirring step using an
ultrasonic probe.

20. The method according to claim 15, comprising spraying, spinning or
dipping of the stable mixed dispersion onto a substrate.

21. The method according to claim 20, wherein the substrates being
selected from the group consisting of platinized single crystal, ITO
coated glass, low refractory metal foils, polymer plates, stainless steel
and carbon steel plates, and polycrystalline ceramic substrates.

22. The method according to claim 20, comprising a drying step, through
heating the suspension derived film at a temperature up to 752.degree. F.
(400.degree. C.), during 1 to 300 min.

23. The method according to claim 22, comprising a ultraviolet (UV)
exposure through heating in air or oxygen rich atmosphere of the
suspension derived film at a temperature up to 752.degree. F.
(400.degree. C.) during 1 to 300 min.

24. The method according to claim 22, comprising a drying step using an
ultrahigh-pressure mercury arc ultraviolet (UV) lamp.

25. The method according to claim 22, comprising a crystallization
through heating the suspension derived film in air or oxygen rich
atmosphere, at a temperature up to 752.degree. F. (400.degree. C.) during
1 to 300 min, and preferably using Rapid Thermal Annealing (RTA).

26. The method according to claim 1, wherein the repetition of steps from
(c) to (e) producing crack-free polycrystalline films with thickness from
50 to 500 nm.

27. The method as claimed in claim 1, the method being applied to
microelectronics and optics industries to fabricate thin film capacitors
for embedded applications, ferroelectric memories to substitute
semiconductor memories, ferroelectric thin film wave guides and optic
memory displays, surface acoustic wave substrates, pyroelectric sensors,
microelectromechanical systems (MEMs), impact printer head as well as
displacement transducers where low-cost and non-refractive substrate can
be used for cost-effective products.

28. PZT films directly processed by the method according to claim 1,
wherein the films have remnant polarization value of 5-15 m C/cm2,
and maximum polarization varying between 10 to 23 m C/cm.sup.2.

Description:

FIELD OF INVENTION

[0001] This invention provides the manufacture of ferroelectric
crystalline metal oxide thin films by means of a low cost chemical
solution deposition method that involves the use of low thermal budgets.

[0002] Specifically, this invention is related to the production of
ferroelectric polycrystalline thin films (<500 nm) on selected
substrates (semiconductors, metals, polymers, etc), by the combination of
the photochemical solution deposition technique (PCSD) and the seeded
diphasic sol-gel process (SDSG). More particularly this invention is
related to the disclosure of a technique for depositing polycrystalline
ferroelectric thin films such as lead ziconate titanate
(PbZr1-xTixO3, PZT) (and others) on different substrates
and with thickness higher than 100 nm and lower than 500 nm, at
temperatures lower than 400° C. for integration with
microelectronic and micromechanical devices, e.g. MEMS
(Micro-Electro-Mechanical Systems), FRAM (Ferroelectric Random Access
Memories) or DRAM (Dynamic Random Access Memories) and flexible
microelectronics.

SUMMARY OF THE INVENTION

[0003] The present invention provides a method of fabrication of
ferroelectric crystalline metal oxide thin films with well-defined
properties at crystallization temperatures lower than those referred in
the literature using a chemical solution deposition approach and the
combination of the two low temperature synthesis methods, previously
developed separately by the inventors: the Photo Chemical Solution
Deposition (PCSD) and the Seeded Diphasic Sol Gel (SDSG). The combination
of the nucleation of the crystalline phase in the films at low
temperatures, by the photo-activation of the precursors chemistry, in
addition to the simultaneous promotion of the crystallization, by
introducing nanocrystalline nucleus, allows the preparation of
crystalline ferroelectric films at low temperature (<400° C.)
with well-defined dielectric and ferroelectric response.

STATE OF THE ART

[0004] Ferroelectric (FE) thin films (TF) have received wide attention
because of their growing use in many applications in microelectronics
devices [1,2]. Their high dielectric constants have been used in Dynamic
Random Access Memories, DRAMs, the possibility of reverting the
spontaneous polarization under the electric field has been employed in
the fabrication of Non Volatile Ferroelectric Random Access Memories,
NVFERAMs, MicroElectroMechanical Systems, MEMS, and NanoElectroMechanical
Systems, NEMS make use of their piezoelectric activity, the pyroelectric
response is the basis of infrared sensors, and more recently the
tunability of the dielectric permittivity with the electric field is
being exploited in tunable microwave devices [3].

[0005] The solid solution between lead titanate (PbTiO3) and lead
zirconate (PbZrO3) (Pb(ZrxTi1-x)O3), known as PZT, is
presently the most commonly used compositional system for piezoelectric
applications with a high technological interest. Within the so-called
morphotropic phase boundary (MPB), that occurs for the composition of
Pb(Zr0.52Ti0.48)O3 (PZT 52/48), PZT exhibits enhanced
dielectric and piezoelectric properties [4]. It is believed that due to
the 14 possible directions of polarisation (eight [111] directions for
the rhombohedral phase and six [001] directions for the tetragonal phase)
in MPB compositions the reorientation of the polar axis is facilitated
and the electrical properties enhanced [5,6].

[0006] Film fabrication techniques can be divided into two general
classes: physical vapour deposition (PVD) techniques and chemical
deposition techniques, this including chemical vapour deposition (CVD)
and chemical solution deposition (CSD). In the former, atoms from a
source are transferred in a continuous and controlled manner under a
vacuum atmosphere (>10-5 Torr) to the substrate, in which the
nucleation and growth of the film occurs atomistically. Depending on how
the particles (atoms or ions) are removed from the target, the following
PVD techniques are considered: rf sputtering, ion beam sputtering,
electron beam evaporation and laser ablation, among others. The former
allows for careful control of film thickness and orientation, and
compatibility with the semiconductor integrated circuit processing. The
difficulty in controlling the stoichiometry of multicomponent films, the
slow rates of deposition (normally around 1 Å/s), the need for
high-temperature post-deposition crystallization annealing and the high
cost related with equipment acquisition and maintenance are the main
disadvantages of these methods [7].

[0007] Chemical methods allow higher deposition rates, good stoichiometry
control, and the production of large area defect-free films when compared
with the previous ones. Chemical vapour deposition (CVD) is very
attractive for industrial manufacturing of conformal functional films.
However, the expensive equipment, limited availability and toxicity of
sources of precursors for functional materials restrict the use of this
technology. On the other hand, chemical solution deposition (CSD)
methods, specially sol-gel, have been increasingly used for the
preparation of films of functional materials. CSD techniques do not
require vacuum ambience, are cheaper and faster, allow for a good
stoichiometry control and production of large area defect-free films with
good properties, although the texture degree of the film is inferior to
that of films prepared by PVD. Wet chemical methods entail the
preparation of the solution, the deposition of the solution onto the
substrate by dip- or spin-coating and the subsequent thermal treatment of
the as-deposited amorphous layer to remove the organics and to achieve
the crystallization and densification of the coatings. Wet processes
comprise sol-gel, metalorganic decomposition (MOD), electrochemical
reaction and hydrothermal routes [8-13].

[0008] The crystallization temperature of post deposition heat treatment
is a key parameter in the preparation of FE films by CSD. Many of the
perovskite thin films are crystallized at temperatures well above
600° C., which degrade underlying electronics, semiconductor
substrate or their metallization layers. For example, the heat treatment
temperature of fabrication of sol-gel PZT films is around 650° C.
to insure good dielectric properties, which constitutes a major drawback
for PZT films integration. The low temperature synthesis of FE TF is then
of paramount significance and more recently it became even more important
due to the promising applications that can be envisaged if FE TF will be
compatible with low cost low melting temperature flexible and rigid
metallic and polymeric substrates.

[0009] For several years now the low temperature synthesis of
ferroelectric thin/thick films has been attempted with modifications at
the `precursor/green state film level` and at the `post deposition
processing level`. Concerning the modifications at the `post deposition
processing level` the most widely used is processing under rapid thermal
annealing (RTA), thus transferring to ferroelectric films a processing
technology typical of the semiconductor industry [14,15]. RTA of
lead-based perovskite films minimizes the formation of
fluorite/pyrochlore intermediate phases, detrimental substrate/film
interfaces or volatilization of lead. Also, it greatly reduces the
thermal budget required for crystallization, although the required
process temperatures are still too high for some applications [1,6]. In
the mean time other alternative methods such as laser-assisted
crystallisation [16-19] or laser lift-off [20] are being used for the
preparation of FE TF. The first one makes use of the local heating
generated by the laser for the crystallisation of the electroceramic
layer. The last one implies the fabrication of the crystalline layer onto
a UV-transparent host-substrate at a high temperature (1000° C.)
and then a transference to the semiconductor substrate by UV laser
radiation at a low temperature (˜100° C.). Extensive and
uniform films are not obtained by these methods, which difficult their
industrial utilization.

[0010] Within the first set of modifications (at the `precursor/green
state film level`), the use of seed-layers and of excess of the volatile
components (e.g. excess PbO in lead zirconate titanate (PZT) and
lead-contained system; Bi2O3 in strontium bismuth tantalate
(SBT) and bismuth-containing system) or the combination of both, are
widely reported in the literature. By using a lead titanate (PT) seed
layer, the perovskite crystallization temperature was reported to
decrease from 600° C. to 550° C. for 15 min for PZT TF
[21]. With a PT seeded layer plus 50 mol % excess PbO, a single
perovskite phase of PZT (53/47) films was obtained on Pt/Ti/SiO2/Si
at 500° C. for 2 h [22]. Perovskite crystallization temperature of
440° C. for 100 min for PZT (30/70) films has also been reported
and it is attributed to the formation of a PtxPb interlayer [23]. By
using 10% excess PbO and either a 10-nm PT or TiO2 nucleation layer,
perovskite crystallization at 400° C. for 5 min for PZT (30/70)
and PLZT (5/30/70) has been reported [24]. Precursor solutions containing
Bi2SiO5 with large molar ratios of this compound to the
ferroelectric phase make possible the CSD crystallization of
ferroelectric thin films at temperatures by 150-200° C. lower than
those of the original ferroelectric layer [25]. Concomitantly, the
control of the solution chemistry to increase the homogeneity at the
molecular level and thus, reactivity of the precursor has been used for
the preparation of ferroelectric thin films at low temperatures as well
In this way, PZT crystalline thin films in the titanium rich part have
been obtained at ˜450° C. for very long annealing times and
at 550° C. in the MPB region; similarly lead-free films (e.g.
SrBi2Ta2O9) have been also prepared at ˜600°
C.

[0011] In general, the ferroelectric response of the films prepared by
these low temperature methods is very weak, clearly denoting the
incipient degree of crystallization of the perovskite films, what
supports the reported need to post heat treat the films at higher
temperatures.

[0012] The PhotoChemical Solution Deposition (PCSD) is based on previous
literature that reported the formation of light-sensitive materials by
using sol-gel process combined with UV irradiation [28, 29]. Single oxide
films such as Ta2O5, ZrO2 or SiO2 have been prepared
by this method at relatively low temperatures [30]. In the case of
ferroelectric multioxide films, UV irradiation of sol-gel deposited
layers has been used for the photo-patterning of the films [32-35].
Recently, PCSD was used and exploited for the fabrication of lead
titanate based perovskite thin films by the Spanish Group [36]. PCSD is
based on the use of sol gel precursors sensitive to the UV light [37] and
on the use of UV radiation sources of high intensity (excimers lamps)
[38] to catalyse the chemical reactions within the precursors towards the
oxide crystallization. The photo excitation of certain organic compounds
present in the sol-gel precursor solutions favours a rapid dissociation
of alquil group-oxygen, reducing the temperature of formation of
metal-oxygen-metal (M-O-M) of the final oxide material. This PCSD
technique is available at the Spanish group and for that the group
designed and constructed a laboratory-scale equipment that consists of a
UV excimer lamp, which is assembled with a IR heating system (UV-assisted
Rapid Thermal Annealing). This irradiation system can be combined with
thermal treatments of the films at low temperatures in a commercial RTA
equipment. The design of this laboratory-scale equipment is based on a
UV-assisted RTA processor (Qualiflow Therm.--Jipelec. www.jipelec.com)
currently commercialised by Jipelec that was developed with the
participation of the Spanish inventors, in the frame of the EU
BRPR-CT98-0777 Project `Microfabrication with UltraViolet-Assisted
Sol-gel Technology, MUVAST`. This processor is now used for the
densification and crystallization of sol-gel, MOD (metallorganic
deposition), CSD and MOCVD (metallorganic chemical vapour deposition)
layers. Using PCSD, ferroelectric lead titanate (PbTiO3, PT) and
modified PT (lead substituted by alkaline earth or lanthanide cations)
thin films were prepared at temperatures over 450° C. onto
Si-based substrates [39-42]. This approach has not been used for the
low-temperature fabrication of PZT or any other lead free multi-oxide
ferroelectric thin films.

[0013] Alternatively, the Portuguese Group has reported pure perovskite
phase formation in PZT (52/48) films at 410° C. for 30 h and
550° C. for 30 min by using seeded diphasic sol-gel (SDSG)
precursors [43]. The crystallization kinetics of PZT (52/48) films was
studied and the overall activation energy was reduced from 219 kJ/mol
(unseeded) to 174 kJ/mol for 1 wt % seeded PZT film and to 146 kJ/mol for
5 wt % seeded films [44]. The early stage of crystallization, structure,
and microstructural development and electrical properties have been
systematically investigated in these FE TF heat-treated at low
temperatures ˜400° C. [45-47]. In this methodology
perovskite nanometric particles are dispersed in the amorphous precursor
and will act as seeds to promote the nucleation of the perovskite phase
in the thin films at low temperatures. Perovskite PZT monophasic thin
films were synthesised at 410° C., when using 5 mol % of seeds
(600-700° C. are regular temperatures to obtain single phase MPB
PZT films without seeds) [46]. Concomitantly BST thin films were prepared
by this technique at 600° C. as well, (700-800° C. are
regular temperatures to obtain single phase BST without seeds) [48]. Due
to the presence of nanometric particles, the kinetics of the phase
crystallization is enhanced and the total activation energy for the
perovskite phase formation was reduced, the multiple nucleation centers
generated by the seeds change markedly the microstructure of the films
and, as a consequence, improved their electrical properties. PZT thin
films prepared at 430° C. by SDSG exhibit reasonable ferroelectric
properties adequate for applications that require metallic or even
polymeric substrates [45,46]. In comparison with non seeded films
ferroelectric response was even obtained for BST seeded films prepared at
a 650° C. via SDSG [48].

[0014] These two techniques, PCSD and SDSG, have been proved to be low
cost approaches for the synthesis of FE TF at low temperatures, but the
combination of these techniques for the preparation of thin films has not
yet been tried. Indeed, the combination of the nucleation of the
crystalline phase at low temperatures, for example by the modification of
the precursors chemistry, with the simultaneous promotion of the
crystallization, for example by introducing nanocrystalline nucleus looks
highly promising, for a reliable integration of FE TF with semiconductor
substrates at temperatures compatible with those used in the
Si-technology [49], as well as with other low melting temperature
substrates; e.g. polymers and metal, opening the possible use of oxide
based ferroelectric materials on the emerging flexible microelectronics
[50].

[0073] A new processing technology to fabricate ferroelectric thin films
at low temperatures, lower than 400° C. for the case of PZT thin
films, with optimised ferroelectric response, and the ferroelectric thin
films directly and indirectly obtained by this technology. This
methodology involves the combination of Seeded Diphasic Sol-Gel (SDSG)
precursors and PhotoChemical Solution Deposition (PCSD).

[0074] The development of a fabrication method of ferroelectric films at
low temperatures is compatible with a wide range of non-refractory
substrates (semiconductors, polycrystalline ceramics, glass, metal and
polymers).

BRIEF STATEMENT OF THE INVENTION

[0075] A processing technology for the fabrication at low temperatures of
ferroelectric crystalline oxide thin films, among others
PbZrxTi1-xO3 (PZT) (<400° C. for PZT) with
ferroelectric properties appropriate for integration in devices is
disclosed. The method is also valid for the fabrication of ferroelectric
thin films of bronze tungsten (A2B2O6), perovskite
(ABO3), pyrochlore (A2B2O7) and bismuth-layer
(Bi4Ti3O12) structures, in which A and B are mono, bi-,
tri-, tetra- and pentavalent ions. The method is based on the combination
of SDSG precursors with PCSD methodology. This invention provides a
method for the fabrication of polycrystalline ferroelectric,
piezoelectric, pyroelectric and dielectric thin films, dense and without
cracks with thickness above 50 nm and below 800 nm on single crystal,
polycrystalline, amorphous, metallic and polymeric substrates at low
temperatures and with optimised properties and it comprises the main
following steps:

[0076] i) synthesis of a modified metal-organic precursor solution of the
desired metal oxide composition with a large photo-sensitivity in the UV
wavelength range;

[0077] ii) preparation by a sol gel process of nanoparticles of the
desired composition, similar or dissimilar to the crystalline compound to
be obtained from the previous precursor sol;

[0078] iii) dispersion by the use of a dispersant agent and
ultrasonication of the former crystalline nanoparticles in the precursor
sol to prepare a stable and homogeneous sol-gel based suspension;

[0079] iv) deposition of the previous suspension onto substrates by either
dip, spin or spray process, followed by drying and partial pyrolysis with
heat treatment;

[0080] v) UV irradiation in air or oxygen of the deposited layer and
further thermal treatment in air or oxygen of the irradiated layer at
temperatures below 400° C.;

[0082] The method here disclosed comprises as a first step the preparation
of a sol gel precursor of the required metallic elements and modified to
make it UV sensitive. For that, the metal alkoxides of Ti(IV) and Zr(IV)
are modified with a b-diketonate (e.g. acetylacetone,
CH3COCH2COCH3). These modified titanium and zirconium
alkoxides are reacted with lead acetate in an alcoholic medium (e.g.
ethanol, C2H5OH), obtaining the PZT sol precursor. This sol has
an enhanced UV absorption, as shown in FIG. 1, thus proving its
photosensitivity under UV light.

[0083] The preparation of nanoparticles of the required composition is the
second part of the process. The nanoparticles may have the same or
different composition from the precursor sol and are prepared by sol gel
method. The particle size and particle size distribution is a critical
parameter. FIG. 2 represents the particle size distribution of PZT
nanoparticles.

[0084] These nanoparticles will be dispersed by ultrasonication in the
photo-active sol to prepare a stable and homogeneous sol-gel based
suspension. To guarantee an optimized dispersion, organic dispersants may
be used. This suspension may be applied to any type of substrate by
spray, spin or dip coating and followed by heat treatment cycles. The
physical nature of the substrates may vary also from single crystals,
polycrystalline, glass, metals to polymers, being such substrates
preferably selected from the group consisting of platinized single
crystal, Indium-Tin-Oxide ITO coated glass, low refractory metal foils,
polymer plates, stainless steel and carbon steel plates, and
polycrystalline ceramic substrates. Following each cycle of deposition,
the coating is dried on a hot-plate, UV-irradiated and crystallized at
temperatures below 400° C., using low thermal budgets that imply
the use of RTA. Irradiation and crystallization may be carried out in air
or oxygen. Deposition, drying, irradiation and crystallization are
repeated until the required thickness is attained as schematically
illustrated in FIG. 3.

[0085] Typical formulations are described below and it is emphasized that
these formulations are not critical but may be widely varied to thin
films of different dielectric materials to be used in microelectronic
devices. PZT films processed by this method have the remnant polarization
value of 5-15 m C/cm2, and maximum polarization varying between 10
to 23 m C/cm2, comparable to those of films processed by
conventional methods at higher temperatures.

[0086] Besides the PZT composition, some examples of other film
compositions that can be fabricated by the method herein disclosed
include generally complex oxides of titanates, niobates, tantalates,
zirconates, tungstates and bismuth based of the of bronze tungsten
(A2B2O6), perovskite (ABO3), pyrochlore
(A2B2O7) and bismuth-layer (Bi4Ti3O12)
structures, in which A and B are mono, bi-, tri-, tetra- and pentavalent
ions, to which this discovery is extended.

[0087] Preparation of the Metal Organic Based Sols

[0088] 1. Photosensitive PbZr1-xTixO3 Sols

[0089] As an example, a sol with x=0.48, PZT52/48, not containing any
excess of lead.

[0090] Sols with an equivalent concentration of 0.2 moles of
PbZr1-xTixO3 per litre of liquid are synthesized by using
as reagents commercial titanium bis-acetylacetonate diisopropoxide
(Ti(OC3H7)2(CH3COCHCOCH3)2, zirconium
tetra-isopropoxide (Zr(OC3H7)4), lead acetate
(Pb(CH3CO2)2.3H2O and an alcoholic medium (ethanol,
C2H5OH). Molar ratios of Ti/Zr/Pb of 0.48/0.52/1.00 are used.
Acetylacetone (AcacH CH3COCH2COCH3) is added to the
Zr(OC3H7)4 in a molar ratio of Zr/AcacH of 1/2. After
heating, a transparent yellowish sol is obtained.

[0091] 2. Preparation of the Sol Gel (Diphasic Sol)

[0092] PZT powders of nanometric dimensions are dispersed in ethanol. This
suspension is added to the photosensitive PZT sol, previously prepared
and this mixture is ultra-sonicated until a stable and homogeneous
suspension is obtained. The particle size varies between 20 to 100 nm.
And the weight percent of powders varies between 0 to 10% of the
suspension weight.

[0093] As a consequence of the combination of the role of the chemically
modified precursors, responsible for the nucleation of the required
crystalline phase at low temperatures with the role of the
nanocrystalline particles to facilitate the nucleation and growth of the
crystalline phase, the films heat treated at these very low temperatures
(375° C. for the case of PZT films) exhibit a well developed
degree of crystallinity as illustrated by the XRD patterns of FIG. 4. The
PZT films prepared at a temperature as low as 375° C. have a
well-defined ferroelectric response, as in comparison with the films
prepared by each of the methodologies independently. FIG. 5 shows the
ferroelectric loops measured in these films. This ferroelectric response
is comparable to that reported for films of the same composition, but
processed at temperatures higher than 600° C.

[0094] The disclosed methodology is applicable to microelectronics and
optics industries to fabricate thin film capacitors for embedded
applications, ferroelectric memories to substitute semiconductor
memories, ferroelectric thin film wave guides and optic memory displays,
surface acoustic wave substrates, pyroelectric sensors,
microelectromechanical systems (MEMs), impact printer head as well as
displacement transducers where low-cost and non-refractive substrate can
be used for cost-effective products.